A LACK of cash could end the only survey dedicated to searching the southern skies for Earth-grazing comets and asteroids.

A LACK of cash could end the only survey dedicated to searching the southern skies for Earth-grazing comets and asteroids. That would create a blind spot in our global view of objects that could cause significant devastation should they hit Earth.

The Siding Spring Survey uses images from the Siding Spring observatory in Australia as part of the global Catalina Sky Survey, an effort to discover and track potentially dangerous near-Earth objects. Astronomers sift through virtually identical images of the sky, looking for moving objects.

Will we see it coming? (Image: Denis Scott/Corbis)

Catalina uses a range of northern hemisphere telescopes - and the Sliding Spring Survey. But in October, Catalina cut off cash to the survey due to growing costs, caused partly by changes in the exchange rate between the Australian and US dollars. That decision was "very difficult", says Steve Larson, who heads Catalina.

Since then, the southern survey has been limping along with temporary funding from the Australian National University in Canberra, but the extension is set to expire at the end of July, says survey operator Rob McNaught.

The leftover building blocks of planets, near-Earth objects orbit the sun in highly elliptical orbits, and sometimes graze or hit Earth. Seeing an asteroid before it hits could save lives by providing time to evacuate a region. "Given the very best circumstances, you can predict an impact to 1 second and 1 kilometre," says McNaught. "There's no other natural disaster that you can do that for."

But without a southern lookout, any object approaching Earth from below 30 degrees latitude would be invisible, says Tim Spahr of the International Astronomical Union's Minor Planet Center in Cambridge, Massachusetts.

That won't be much of a problem for massive objects like the asteroid that wiped out the dinosaurs. These are rare and astronomers estimate they have already found and are tracking 94 per cent of them via software models. The worry is asteroids about 30 metres wide, which could flatten a city. Such a hit is blamed for the Tunguska event in 1908, which levelled a 2000-square-kilometre swathe of forest in Siberia.

There are around a million of these smaller objects, making them the most likely to hit Earth, yet locations for less than 1 per cent of them are known. Without a southern telescope, "you could easily get blindsided by one of these", says Don Yeomans, of NASA's Near-Earth Object Program at the Jet Propulsion Laboratory in Pasadena, California. "Whether that's a 1 per cent, 10 per cent or 20 per cent increased risk, I don't know. But it is an increased risk."

What's more, as most asteroids and comets are tracked across both hemispheres, those discovered in the north could get lost without follow-up from the south. There will also be objects seen in the north that could have been spotted sooner in the south, giving more time to prepare.

McNaught estimates that the survey needs about US$180,000 per year, plus a one-off $30,000 to fix the observatory dome. "I really wish I could tell you that the chances are very good that we'll be able to find some money, but I can't," says Harvey Butcher, who heads the team at Australian National University that is providing temporary funding.

If the survey shuts down, there won't be another ground telescope capable of fulfilling its duties until the 2020s, when the Large Synoptic Survey Telescope is due to go online in Chile.

The non-profit B612 Foundation plans to build a space telescope to scan for small asteroids but it won't launch until at least 2017 (see "The people's asteroid defence"). "In the interim, having one eye closed when the cost of having it open is so little seems to be penny wise and pound foolish," says B612 co-founder Russell Schweickart, a former NASA astronaut.

The people's asteroid defence

Citizens, defend thyselves. As governments prove slow at funding telescopes to monitor asteroids, a non-profit organisation plans to pick up the slack - though its telescope won't launch till 2017 at the earliest.

The B612 Foundation - named for the asteroid that was home to the prince in The Little Prince - has announced a plan to build, fly and operate the first private space telescope. Called Sentinel, it will cost several hundred million dollars, which the foundation hopes to raise through donations.

"We think this is eminently doable," says B612's Ed Lu, a former NASA astronaut, who compares the project to funding museums or concert halls. "This telescope will be owned by the people of the world."

Unlike ground-based surveys, Sentinel will orbit the sun, so its view will not be confined to one hemisphere. It will look in infrared wavelengths, so small asteroids that don't reflect much visible light can be seen via their heat. Planned for launch in 2017 or 2018, Lu predicts that Sentinel will find more asteroids in its first month than all previous telescopes combined.

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